The purpose of this test is to evaluate the operation of an Antilock Braking System (ABS) inductive wheel speed sensor based upon its output voltage and frequency.
Access to individual wheel speed sensors may be difficult.
All wheel speed sensors connect to the ABS control module, which is usually located in the engine bay.
PicoScope can be connected to gather waveforms from 2 or more wheel speed sensors whilst conducting a road test. In these conditions, the computer and screen must be out of the driver's view and/or operated by a second technician.
These waveforms have the following characteristics:
The oscillation frequency and amplitude increase with increasing wheel speed.
Channel A has no gaps or atypical peaks or troughs with an approximately constant wheel rotation speed.
Channel A is as above.
Channel B displays a periodic (about every half a second) abnormality, causing an increased amplitude over a couple cycles. This is typical of a rotating component issue (the sensor is fixed), for example, a damaged reluctor ring.
In addition to Channel A and Channel B described above, Channel C and Channel D have been connected to the remaining wheel speed sensors, with both displaying good waveforms (Channel B remains faulty).
Wheel speed sensors provide wheel and road speed feedback to ABS and its derivative active vehicle safety systems (i.e. stability and traction control systems etc.).
These systems are designed to provide corrective action (e.g. wheel braking or engine torque limitation) when the vehicle or wheel speed(s) have exceeded their normal operational tolerances, for example, during conditions of wheel slip, oversteer or understeer etc. Wheel speed sensors are critical to the operation of these systems and, therefore, the safe handling of a vehicle.
Inductive wheel speed sensors encase a wire coil around a magnetically polarised core and operate in tandem with a pulse wheel mounted on a component rotating at wheel speed, for example, a driveshaft or hub. As the pulse wheel passes the sensor, the sensor's magnetic field is disturbed, which induces an oscillating voltage within the wire coil and the circuit connected to it. The quicker the wheel rotates, the greater the oscillation frequency and amplitude.
An ABS control module expects similar (within a given tolerance) oscillation frequencies from all the vehicle’s wheel speed sensors and uses any differences to calculate the timing and scale of its interventions.
If one or more wheel speed signals continuously fall outside of normal parameters the control module may turn the ABS function off. A driver warning light will be illuminated but, as with any electrical fault on ABS, normal hydraulic braking is maintained.
Wheel speed sensors and their pulse rings are exposed to the elements and have to operate under conditions of constant vibration and movement. As such, common faults are:
Selection of component-related Diagnostic Trouble Codes (DTCs):
C0000 - Vehicle Speed Information Circuit Malfunction
C0035 - Left Front Wheel Speed Circuit Malfunction
C0036 - Left Front Wheel Speed Sensor Circuit Range/Performance
C0040 - Right Front Wheel Speed Circuit Malfunction
C0041 - Right Front Wheel Speed Sensor Circuit Range/Performance
C0045 - Left Rear Wheel Speed Circuit Malfunction
C0046 - Left Rear Wheel Speed Sensor Circuit Range/Performance
C0050 - Right Rear Wheel Speed Circuit Malfunction
C0051 - Right Rear Wheel Speed Sensor Circuit Range/Performance
C0221 - Right Front Wheel Speed Sensor Circuit Open
C0222 - Right Front Wheel Speed Signal Missing
C0223 - Right Front Wheel Speed Signal Erratic
C0225 - Left Front Wheel Speed Sensor Circuit Open
C0226 - Left Front Wheel Speed Signal Missing
C0227 - Left Front Wheel Speed Signal Erratic
C0229 - Drop Out of Front Wheel Speed Signals
C0235 - Rear Wheel Speed Signal Circuit Open
C0236 - Rear Wheel Speed Signal Circuit Missing
C0237 - Rear Wheel Speed Signal Erratic
C0238 - Wheel Speed Mismatch
C0245 - Wheel Speed Sensor Frequency Error
C0300 - Rear Speed Sensor Malfunction
C0305 - Front Speed Sensor Malfunction
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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